The invention pertains to valves which can be controlled from an operator position remote from the valve position. More specifically, the invention pertains to motorized valves of the type having provision for automatically stopping the motor at the end of valve travel.
Many applications require the use of remotely-controlled valves to meter fluids. With the increasing application of microprocessors to all areas of technology, many industries have come to require valves which are adaptable for use with microprocessor control. The size reduction made possible by the microprocessor has also demanded valves which are as small as possible.
It is an object of this invention to provide a valve which is remotely controllable.
It is a further object of the invention to provide a remotely-controlled valve which is particularly suited to control by electronic devices, such as microprocessors.
It is a still further object of the invention to provide a valve which is as compact as possible, while still being able to control high pressures in the range of 5,000 to 100,000 PSI, or more.
Motorized valves are not new. Large electrically-controlled valves were used in steam, water, and gas systems may years ago. Valves of the size used in generating plants or water systems tended to be of the "sluice-gate" type, wherein a plate was lowered into a pipe, blocking the flow of water. Such valves are quite rugged, and the forces used are great, so that a valve may be driven shut without danger of damage. Limit switches at the ends of the valve travel sufficed to shut off the motors, if any automatic shut-off was provided at all. Some devices were equipped with slip-clutches, or overriding clutches, which would allow the motor to turn past the point where the valve had been fully closed or opened. See, for example, Andersen, U.S. Pat. No. 865,556 [1907], or Buescher, U.S. Pat. No. 2,671,331 [1956].
Even in very large valves, however, the use of excessive amounts of torque to "slam" a valve shut, or to continue tightening the valve past the end of its travel, will lead to unnecessary wear. To minimize this, some valve designs included mechanical torque sensing mechanisms, such as spring-loaded cams, to shut off the motor when a torque limit on the shaft was exceeded (Fortner, U.S. Pat. No. 3,675,751 [1972], and Balz, U.S. Pat. No. 3,700,085 [1972]). In valves of the type represented by this invention, however, such mechanical torque sensing devices are not practical due to their size, complexity, and inaccuracy. The small seats used in high-pressure valves could be damaged before a mechanical torque-sensor could respond. Also, mechanical torque-sensors are hard or impossible to adjust to the differing torques required by different pressures being metered, or due to wear or friction in the valve mechanism. This is very critical in smaller valves, especially those for high pressures, where such effects are magnified.
It thus an object of the invention to provide a controller for a small valve especially useful at high pressures which can be operated with minimal wear and tear on the valve due to overtorquing; and which is adjustable to a wide range of valve conditions.
One effective method of determining that the valve has reached the end of its travel is to measure the current supplied to the motor. As the motor is "stalled," the current drawn increases dramatically. This was recognized in a 1909 patent to Kanmacher, U.S. Pat. No. 923,186 which used the overcurrent to draw in a solenoid, unlatching a mechanical switch and stopping the valve motor. Chitty, U.S. Pat. No. 1,734,419 [1929] also looked at current, without providing for automatic shut-off.
The method of determining valve closure by current is, in fact, the most practical method available for use in automatic valve control. When attempting to use the technique in a smaller type valve, however, several problems arise. Driving the motor fully into a "stalled" condition could damage the valve. Also, the current sensing can be "fooled" by the starting surge current of the motor or by increased friction in mid-travel.
Okamura, et al. U.S. Pat. No. 4,099,704 [1978] solve the latter problem by sensing valve position by means of photocells and holes in the valve shaft. The current sensing is only in effect when the valve is "almost" closed. This requires a specially modified valve, adding complication. The current sensing will stop the motor when the current rises above a given point, but only at the end of travel. This can pose problems, however, if the valve were to stick in an intermediate position. In such a case the motor is liable to burn out, or the valve may be damaged, as the current limit will be ignored. Conversely, if the valve encounters resistance toward the end of its travel, the controller cannot cause the motor to re-try the valve closure.
This can become particularly important if the valve were to stall just before complete closure, due perhaps to dirt in, or damage to, the valve. At very high pressures, there might be unusual resistance to valve closure. The operator might need to force the valve shut to stop the flow in the system. He might well decide to do this, regardless of any possible damage to the valve. The control must allow him this option.
It is an object of the invention to provide a controller for valves using current sensing to limit valve torque.
It is a further object of the invention to provide a current-limit controlled valve which is "resettable" to allow re-trial of valves which might stick or stop due to friction or current surges.
Other objects of the invention will become apparent in the more detailed disclosure below.